Transmission Rebuild - Manual

Complete removal, disassembly, inspection, rebuild, and reinstallation of the G56 6-speed manual transmission including clutch replacement and related components.

Warnings

Tools required

Parts

• G56 transmission rebuild kit (bearings, seals, gaskets, synchronizers) × 1 — Use OEM specification
• Clutch disc (13-inch dual disc for Cummins) × 1 — Use OEM or equivalent rated for diesel torque
• Pressure plate assembly × 1 — Use OEM or equivalent rated for diesel torque
• Release bearing (throwout bearing) × 1 — Use OEM specification
• Pilot bearing × 1 — Use OEM specification
• Input shaft seal × 1 — Use OEM specification
• Output shaft seal × 1 — Use OEM specification
• Shift tower gasket/seal kit × 1 — Use OEM specification
• Transfer case adapter gasket × 1 — Use OEM specification
• Transmission case RTV sealant (Mopar specified) × 1 — Use OEM specification
• Clutch hydraulic line (if damaged) × 1 — Inspect and replace as needed
• Transmission mount × 1 — Inspect and replace if worn
• Transfer case output seal × 1 — Use OEM specification

Fluids

• ATF+4 — 8 qt

Preparation

1. Disconnect negative battery cable and secure away from terminal
2. Raise vehicle on lift or use jack stands at frame rails to achieve safe working height
3. Remove skid plates and belly pans if equipped
4. Drain transmission fluid into suitable container by removing drain plug
5. Drain transfer case fluid into suitable container
6. Mark driveshaft orientations with paint or marker before removal for proper reinstallation
7. Remove front and rear driveshafts and cap transfer case outputs
8. Disconnect shift linkage and mark positions
9. Disconnect hydraulic clutch line at transmission bellhousing
10. Support engine with jack or engine support bar from above
11. Remove exhaust system components interfering with transmission removal (typically downpipe to mid-pipe section)
12. Clean work area and organize parts storage bins for small components

Procedure

1. 1

   Remove transmission crossmember and supports
   Support transmission and transfer case assembly with transmission jack. Remove transmission mount bolts and crossmember mounting bolts. Carefully lower crossmember away from vehicle. Keep slight upward pressure on transmission jack throughout process. G56 manual transmission fluid (Mopar-specified / GL-4) plus ATF+4 for transfer case
2. 2

   Disconnect electrical connections and remove transfer case
   Disconnect the output shaft speed sensor, reverse light switch, and any other electrical connections at the transmission and transfer case. Remove transfer case-to-transmission mounting bolts (typically 6 bolts). Use second jack or stand to support transfer case independently. Carefully separate transfer case from transmission output shaft and lower away. Be prepared for residual fluid spillage.
3. 3

   Remove transmission from vehicle
   Remove bellhousing-to-engine block bolts (typically 6-8 bolts around perimeter). Verify all electrical connections, linkages, and lines are disconnected. Carefully slide transmission rearward off input shaft, ensuring clutch remains supported. The transmission must slide straight back to avoid damaging clutch disc or input shaft. Lower transmission on jack and remove from under vehicle.
4. 4

   Remove and inspect clutch assembly
   With transmission removed, inspect clutch for wear, hot spots, or oil contamination. Remove pressure plate mounting bolts in star pattern, loosening gradually to prevent warping. Remove pressure plate and clutch disc. Inspect flywheel for heat cracks, scoring, or glazing. Check flywheel runout with dial indicator against the factory specification (verify exact limit; commonly approximately 0.005 inches). Remove and replace pilot bearing from crankshaft using puller or slide hammer. Resurface or replace flywheel if damaged.
5. 5

   Disassemble transmission external components
   Mount transmission securely on bench or holding fixture. Remove shift tower assembly and note shift fork positions. Remove rear extension housing bolts and carefully separate housing from case. Remove output shaft seal and, if present, the speed sensor drive/tone ring assembly. Remove front bearing retainer and input shaft seal. Document all component positions with photos or notes.
6. 6

   Split transmission case and remove gear assemblies
   Remove case bolts in proper sequence (typically perimeter bolts first, then internal bolts). Carefully pry case halves apart using designated pry points only. Remove mainshaft assembly with synchronizers and gears intact. Remove countershaft assembly. Remove input shaft from front of case. Keep all bearings, shims, and races with their respective shafts.
7. 7

   Disassemble and measure internal components
   Disassemble mainshaft by removing snap rings and sliding gears, synchronizer assemblies, and bearings off shaft. Note orientation and order of all components. Use hydraulic press to remove pressed bearings. Measure all gear teeth for wear using micrometer. Check synchronizer cone surfaces for scoring or excessive wear (5th and 6th are critical). Measure all bearing journals and races for out-of-round or wear. Check all shift forks for wear at engagement points. Measure mainshaft and countershaft runout with dial indicator (maximum 0.002 inches).
8. 8

   Clean and inspect all transmission components
   Thoroughly clean all metal components in solvent tank. Inspect case halves for cracks, especially around bearing bores and bolt holes. Check all gear teeth for chipping, pitting, or excessive wear. Inspect synchronizer rings for cone wear (replace if wear step exceeds specification). Check all bearing surfaces for pitting or spalling. Verify shift rail bores are not worn or scored. Replace any components not meeting specifications per rebuild kit instructions.
9. 9

   Reassemble mainshaft and countershaft with new components
   Press new bearings onto shafts using proper driver sleeves on inner races only. Install gears and synchronizer assemblies in documented order. Install new synchronizer rings and verify proper engagement gap with feeler gauge. Secure components with new snap rings, ensuring full seating in grooves. Apply thin coat of the specified G56 manual transmission fluid to all moving parts during assembly. Verify smooth rotation of all gears after assembly.
10. 10

    Reassemble transmission case halves
    Install mainshaft and countershaft assemblies into main case half. Install new bearings in case bores if required. Apply thin bead of specified RTV sealant to case mating surface. Carefully position second case half and align dowel pins. Install case bolts and tighten in proper sequence (typically crisscross pattern from center outward). Allow sealant to cure per manufacturer specifications before adding fluid.
11. 11

    Install extension housing and shift tower
    Install new output shaft seal in extension housing using seal driver. Apply RTV to housing mating surface and install onto case. Install shift tower with new gasket or seal. Verify shift forks engage properly with synchronizer sleeves. Test shift operation by hand through all gears, confirming smooth engagement.
12. 12

    Install front bearing retainer and input shaft seal
    Install new input shaft seal in bearing retainer using seal driver. Apply RTV to retainer mating surface and install onto case. Verify input shaft rotates freely and has minimal end play. Reinstall the output speed sensor and any associated tone ring/retainer as applicable.
13. 13

    Install new clutch assembly
    Install new pilot bearing in crankshaft using driver that contacts outer race only. Clean flywheel surface with brake cleaner. Position clutch disc on flywheel with longer hub side toward transmission. Use clutch alignment tool through disc and into pilot bearing. Position pressure plate over disc and install mounting bolts finger-tight. Tighten pressure plate bolts in star pattern to proper specification. Remove alignment tool and verify disc is centered.
14. 14

    Install transmission into vehicle
    Apply thin coat of high-temperature grease to input shaft splines and release bearing contact surfaces. Position transmission on jack and raise into position. Align input shaft with clutch disc splines using alignment tool as guide if needed. Slide transmission forward onto dowel pins and fully seat bellhousing to engine block. Install bellhousing bolts and tighten to specification. Connect hydraulic clutch line and bleed system if needed.
15. 15

    Install transfer case and complete assembly
    Clean transfer case adapter surface and install new gasket. Position transfer case on jack and align with transmission output shaft. Slide transfer case onto transmission and install mounting bolts to specification. Install crossmember and transmission mount, tightening all fasteners to specification. Connect all electrical connectors including speed sensors and reverse light switch. Install driveshafts in original orientations. Reconnect shift linkage and verify proper gate operation. Install exhaust components and skid plates.

Reassembly

1. Fill transmission with 8 quarts of ATF+4 through fill plug until fluid reaches bottom of fill hole
2. Fill transfer case with 2.5 quarts of ATF+4
3. Reconnect battery negative cable
4. Bleed clutch hydraulic system if line was disconnected
5. Check all fluid levels and inspect for leaks before test drive

Verification

• Start engine and verify no unusual noises from transmission or transfer case
• Depress clutch and verify smooth engagement without chatter or slippage
• Test shift operation through all gears with engine running and vehicle stationary
• Perform test drive and verify smooth shifting under load in all gears
• Check for proper clutch engagement point and verify no slippage under acceleration
• Verify 4WD engagement and disengagement functions properly
• Recheck all fluid levels after test drive and inspect for leaks at all seals and case mating surfaces
• Verify speedometer operation if equipped with mechanical drive
• Road test through all gears including highway speeds to verify 5th and 6th gear operation
• Listen for any bearing noise, gear whine, or synchronizer issues during operation

Related trouble codes on this vehicle

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